The present invention relates generally to television systems. More particularly, the present invention relates to improved definition television systems which seek to provide a higher quality picture from now-standard broadcast signals. Even more particularly, the present invention seeks to provide improved video signal processing and noise immunity characteristics in response to signal content to provide desired improvements in picture display.
High definition or enhanced definition television ("HDTV") systems seek to provide a higher quality television picture by improving the characteristics of the broadcast or transmitted signal. Several such systems are now known; all, to date, require additional electromagnetic spectrum bandwidth to provide the enhanced broadcast signals. In contrast, improved definition television systems seek to provide a higher quality television picture by improving the characteristics of the signal processing at the television receiver. Improved definition systems seek to give a better picture within present broadcast standards, e.g., the six megahertz (6 mhz.) per channel standard in the NTSC system.
Standard video signal processing uses some type of filtering to separate or comb the 3.58 megahertz color carrier signal from the 4.25 megahertz bandwidth luma signal. Desirably, the implemented filtering prevents artifacts or distortions in the displayed picture. Without some filtering, the amplitude modulated color signal can produce a grid appearance on the screen in response to chroma signals that are mistakenly recognized as and then processed as luma signals.
However, several known filtering techniques each can introduce undesired artifacts in the displayed picture. For example, the simplest filtering technique, notch filtering, can undesirably reduce resolution. A notch filter removes video signal in a notch surrounding the 3.58 megahertz chroma carrier. Alternately, a notch filter provides luma in the bandwidth of zero to about 3.1 mhz. However, that also removes luma within the same region or above the filter cutoff frequency, thereby reducing horizontal resolution. This becomes readily apparent when the television camera pans back from a structure, such as a tall office building, comprised of many smaller, horizontal elements, such as windows; at some point the building and windows will become blurred--that point occurring when the level of detail necessary to resolve the window edges passes into the notch above about 3.1 MHz.
Alternate filtering techniques include line filters. Such filters rely on the known characteristic R of standard video signals that alternate lines of each picture have opposite polarity chroma signals. Pure luma may be extracted by adding the video signals for adjacent lines (typically stored in a line buffer or memory), thereby cancelling chroma. However, this does not always work; for example, when one line has no chroma, simply adding it to the next line will not cancel the chroma. This creates a loss of vertical resolution and gives the appearance of "hanging dots" on the screen. The hanging dots appear in a zipper pattern which seems to move back and forth on the screen as the non-cancelled chroma information is processed as luma.
One other method is known as frame filtering or combing. This technique relies on another known characteristic of standard video signals, namely that the same line in alternate frames carries chroma of opposite phase. However, this technique can only be used when succeeding frames have identical video content. If not, then the displayed picture is undesirably distorted.
Of course, any filtering technique must completely separate the chroma information for chroma processing. In the worst case, an inadequate filter can result in luma being interpreted as chroma. This creates highly undesirable cross chrominance in the displayed picture. Likewise, noise in the television signal can undesirably affect the processing of the luma and chroma components.
Each of the known and described filtering techniques provides adequate performance and an acceptable display in some circumstances. However, each suffers drawbacks or inadequacies as described in the foregoing examples. Accordingly, the present invention seeks to provide an improved signal processing technique that generally overcomes the deficiencies of the prior art and provides improved picture display. The present invention lies, in part and fundamentally, upon recognizing actual picture content13 within selected noise levels.
A further object of the present invention lies in the implementation of techniques for choosing one or more processing methods in response to received video signals.
A further object of the present invention lies in providing an improved picture quality based upon actual picture content.
A further object of the present invention is to provide enhanced video signal processing through recognition of selected characteristics in the video content of received picture signals.
Another object of the present invention lies in providing improved displayed picture quality through reduced noise susceptibility in chroma/luma processing. A broader related object lies in improving noise immunity in composite video processing.
Yet a further object of the present invention is to provide a motion detection technique for improved signal processing to provide an improved picture display.